THE EVOLUTION OF THE HUMAN HAND

THE EVOLUTION OF
THE HUMAN HAND
THE ROLE OF TOOLS
Name
Date

THE GREAT DEBATE
Since the discovery of fossil hand bones of our human ancestor Homo habilis
alongside core tools at Olduvai Gorge in the early 60’s, the evolution of the human
hand has been a source of great speculation and debate (Marzke 1). There have
been many theories as to how and why the hand evolved the way it did, however
there appears to be one dominate and most plausible theory: the role and use of
tools in our early ancestral culture. It is proposed that it was tools that
revolutionized the human hand, fueling the evolution that has produced the modern
human hand. This presentation will give insight into how the human hand has
evolved and how the role of tools influenced this evolution.

JUST WHAT HAS HAPPENED?
To understand how these changes have unfolded, it is important to first
understand exactly WHAT changes have taken place. To do so, we will
take a look at the distinguishing factors of the modern human hand, the
functioning they serve and how they apply to tool making. Once we
understand the changes and the purpose they served, we will discuss how
this remodeling of the human hand was made possible by the
reproductive advantages it allowed. Finally, we will discuss the variable
factors we must consider for this theory to be true.

DISTINCT FUNCTIONING
According to Dr. Mary W.
Marzke of the Arizona
State University
Department of
Anthropology, the
functions that make the
human hand so distinctive
are the ability to firmly
grasp objects and cup the
hand around them in a
manor that increases
precision and
maneuverability (Marzke
1). It is this same precision
and maneuverability that
allows us to engage in
more advanced tool
making activities. Also,
although not as advanced
in comparison, it was the
evolution of the
mechanisms that provide
us with these abilities that
allowed our ancestors to
engage in core tool
making. In the following
slides we will take a
comprehensive look at the
areas of the hand that have
evolved to allow this.

THE MODERN HUMAN HAND
The features of the
modern human hand that
allow such unique
precision and
maneuverability for tool
making can be summed
up in 6 main points. For
greater understanding of
these distinctions, I will
highlight the areas
mentioned on the
following diagram.

DEFINING ANATOMICAL FEATURES
OPPOSABILITY AND LENGTH OF THUMB
Opposability, the ability to
touch ones thumb to the
fingertips of all fingers on
the same hand, is indeed a
trait we share with the
apes; however, it is an
essential to our ability to
cup and grip items firmly
in order to manipulate
them (Marzke 123).
According to Dr. Richard
W. Young of the
University of California,
the human thumb also
displays greater mobility
in comparison to other
primates (Young 165). In
addition, the human
thumb has larger muscles
and the presence of the
flexor pollicis longus
muscle
which is absent in chimps
(Young 167). These
muscles provide added
strength and control to
thumb movement (Young
167) .Another factor that
makes the human thumb
distinct from other
primates is the fact that in
proportion to the rest of
the hand, the thumb is
much longer in
comparison with other
primates (Young 165).

DEFINING ANATOMICAL FEATURES
COMPLEXITY IN THE WRIST
Within the modern
human wrist there
exists many
complexities; however,
for the purpose of
grasping for tool
making, there is two
aspects of the wrist
that are especially
significant. First, the
base of the second
metacarpal is
extremely complex,
allowing connectivity
to three carpal bones,
the trapezium, the
trapezoid and the
capitate (Markze 123).
This compound
connectivity allows
for pronunciation of
the metacarpal (123).
Also, the broadness
of the trapezoid and
capitate in association
work to relieve the
stresses that form due
to the opposition of
the thumb to the
fingers during
manipulation of
itemry (Marzke 123).

DEFINING ANATOMICAL FEATURES
MARKED ASYMMETRY
A feature that is
vital to the ability
to grasp firmly and
efficiently during
tool making is
made possible by
the distinct shapes
of the second and
fifth metacarpal
heads (Marzke
123). The fact that
these two
metacarpals have
heads that are
asymmetrical to each
other and have
distinct projections
on the outer areas
enables these fingers
to rotate toward
each other during
flexion of tendons
(Marzke 123). This
reciprocal motion
permits the hand to
form around an item
and grip more firmly
for manipulation.

DEFINING ANATOMICAL FEATURES
AN AID IN ROTATION
Contributing to that
reciprocal rotation
between the second
and fifth metacarpals
and therefore
contributing to the
overall strength and
precision of the grip
it provides for is a
unique saddle joint
between the fifth
metacarpal base and the
hamate (Marzke 123).
This saddle joint also
permits greater rotation
for connectivity of the
fifth phalange to the
thumb (Bade 116). This
increase in range
provides greater overall
dexterity (Bade 120).

DEFINING ANATOMICAL FEATURES
SHORT HANDS
As you can see from figure
1 of Dr. Young’s
publication, when
compared to a chimp hand
(a model for our hominid
ancestors) a significant
amount of digital and pad
shortening can be seen in
the human hand (Young
166). This shortening
provides greater stability
and better stress endurance
(Young 167).

GETTING A GRIP ON TOOL MAKING
TWO KINDS OF GRIPS
These evolved sections allow the human hand to grip in two distinct ways
vital to the tool making process. According to Dr. J.R. Napier, with these
advancements, the human hand can accomplish two types of grips, the
precision grip and the power grip (Napier 903). The power grip is
characterized by a clamp like formation in which the fingers and the palm
are partly flexed and counter pressure is applied by the thumb which is in a
position even to the palm (Napier 903). The main objective of this grip in
terms of tool making/using strategies is to absorb impact without injuring
the user, prevent the object from exiting the hand and allow for immediate
restrike (Young 170). The precision grip is accomplished when the object
is pinched between the flexors of the fingers and the thumb which
parallels the middle and distal phalanges (Napier 903). In regards to tool
making and using, this grip is meant to increase precision in throwing, and
allow for a firm yet accessible grip on an object (Young 169). These two
types of grips have also commonly been referred to as the cylinder (power)
and ball (precision) grips.
This image from Napier’s article displays the two grips (Napier
903).

GETTING A GRIP ON TOOL MAKING
Now that we understand the grips evolution has allowed, lets take
a look at how they apply to primitive tool making. As you can see
from figure 11.3 of our course text “Biological Anthropology” by
Michael Alan Park, both precision and power grips were necessary
to make core tools like the ones found at Olduvai Gorge (Park
266). The hand containing the hammerstone is held in a way that
is reminiscent of the power grip, probably in order to control the
striking point and absorb shock, core too is held in a clamp-like
power grip in order to absorb shock without the stone exiting the
hand on impact. The use of these core tools would also have been
impossible without the ability to power grip in the case that they
were used for clubbing and in the case they were used for
throwing to strike an enemy they would have needed precision
grip. These wouldn’t have been the only tools these grips were
vital to, as Young stresses, these grips were also necessary to wield
clubs, and throw stones and other weapons (Young 165).
GRIPS IN ACTION

AN ADVANTAGE IN REPRODUCTION
As we all learned this semester, evolution takes place when a trait causes a
reproductive advantage and is selected for, but just how does this apply to hand
evolution through tools? The answer can be found when we look at the culture
of our more primitive ancestors. As Young notes, males who were highly
aggressive and skilled with weapons like clubs, were the most likely to rise in
dominance hierarchy and gain better access to resources (Young 165). These
resources would include the food and water that insured survival as well as
access to more females for breeding. In males, the most skilled weapons users
were most likely the ones that possessed certain variations within the hand that
better enabled them to use their weapons effectively. In females, possessing
these variations would better enable them to protect their young and
themselves by warding off predators with weaponry, therefore being more likely
to pass on these traits to other generations. (Young 166). With time, the variable
traits that allowed the maximization of use of tools of protection would have
been selected for and accumulated to produce the modern human hand as we
know it.

VARIABLES TO CONSIDER
IT MUST BE TRUE
As viable as this theory seems, there are factors that need to be accounted for in
order for this theory to be true. First, due to limited hand fossils from few hominid
species, the information available is qualitive not quantitive (Marzke 126). Also, not
all of these features have been statistically analyzed for distinct effectiveness in the
functioning they provide (Marzke 126). Similarly, experimentation of the
manipulative advantages of these gripping features are fairly limited (Marzke 126).
Even with these factors in consideration, the likelihood that the information that
has been gathered until present proves this theory is very high; making sense of the
fact that this theory is most accepted.

IN CLOSING
As complex and efficient for tool making and use as the human hand is now, it
wasn’t always this way. The modern human hand and its comprehensive gripping
capabilities are the result of millions of years of evolution by selection. It is
interesting to see that a culture of tools and aggression has produced such a
complex appendage. This also raises many questions such as “Will future
anthropological finds disprove this theory, or confirm it?” and “How will our
current culture and modern tools like cell phones and computers effect the future
evolution of the human hand?”. Lets not wait for the future to answer these
questions, after all, it is the past that truly holds the key.

WORKS CITED
Bade, H, J Koebke, and H Bilger. "[Functional anatomy of the fifth carpometacarpal joint].“ Handchirurgie, Mikrochirurgie,
Plastische Chirurgie: Organ Der Deutschsprachigen Arbeitsgemeinschaft Für Handchirurgie: Organ Der
Deutschsprachigen Arbeitsgemeinschaft Für Mikrochirurgie Der Peripheren Nerven Und
Gefässe: Organ Der Vereinigung Der Deutschen Plastischen Chirurgen 25.3 (1993): 116-120. Web. 18 May 2011.
Marzke, Mary W., and R. F. Marzke. "Evolution of the Human Hand: Approaches to Acquiring, Analyzing and Interpreting
the Anatomical Evidence." Journal of Anatomy 197 (2000): 121-40. Print.
Napier, J. R. "The Prehensile Movements of the Human Hand." The Journal of Bone and Joint Surgery 38B.04 (1956): 902-13.
Print.
Park, Michael Alan. "The Evolution of Genus Homo." Biological Anthropology. 5th ed. Boston: McGraw Hill, 2008. Print.
Young, Richard W. "Evolution of the Human Hand: the Role of Throwing and Clubbing." Journal of Anatomy 202.1 (2003):
165-74. Print.